The invention relates to a method of and a system for writing key information transmitted securely from a central station to a remote station into a data carrier available at said remote station. In a preferred use the data carrier is a key for a motor vehicle, which key is to be issued to the legitimate owner of the motor vehicle by a dealer, for example because the owner requires an additional key or has lost a key originally received upon the purchase of the motor vehicle. However, it is to be noted that the method and the system in accordance with the invention are also suited for other uses, for example for keys giving access to certain rooms or areas. In general, the method and the system in accordance with the invention enable selected allocated information to be written into a data carrier in a secure manner.
When key information stored at a central station is to be written into a data carrier at a remote station it is necessary in conventional systems to ensure that the transmission of the key information to the remote station cannot be overheard, because otherwise an unauthorized person can write the illegally intercepted key information into a data carrier of his own and can thus, for example, gain unauthorized access to protected rooms or areas. The alternative, i.e. to write the key information into the data carrier at the central station and subsequently send it to the remote station, is also unfavorable because the data carrier can be stolen during transportation.
It is an object of the invention to provide a method of securely writing key information into a data carrier which is issued at another station than that where the key information is generated or has been stored.
According to the invention this object is achieved in that the key contains stored identification information which cannot be read externally and is consequently secret, and in that the key information is encrypted with this identification information at the central station and the encrypted information is transferred to the data carrier at the issuing station. In the data carrier this encrypted key information is subsequently decrypted and stored.
This method has the advantage that the data carriers can be despatched freely because they do not contain any key information, so that a thief cannot abuse the data carrier. The unauthorized interception of the transmitted encrypted key information is neither of any avail to an unauthorized person if he does not have a data carrier with the correct identification information into which he can write the encrypted key information.
In this respect is important that each data carrier contains open further identification information, which is readable. Thus, it is possible to store in each data carrier individual identification information which differs from that in the other data carriers, the relationship between the open further identification information and the secret identification information being stored at the central station. Owing to this measure encrypted key information can be decrypted correctly by means of only one, i.e. the correct, data carrier.
In order to enable the allocation of secret identification information, key information and the open further identification information to be organized more easily, it is effective if the identification information and the open identification information are written into the data carrier at a further station before the data carrier is conveyed to the remote station. This further station should then be coupled to the central station via a protected information transmission link, so as to enable the same information to be written in at this station. The further station can also be identical to the central station.
The key information to be transmitted to the data carrier is assigned unambiguously to at least one individual object, for example a motor vehicle. When a data carrier is to be assigned to such an individual object the object information characterizing this object should be transmitted to the central station. In order to also protect this transmission path it is effective to encrypt the object information with the open further identification information prior to the transmission to the central station.
For data encryption a variety of methods are known. A particularly simple encryption and decryption of the key information and the objection information, which can be used in the method in accordance with the invention, is by exoring with the identification information. Since the identification information is secret, decryption is not possible without the key information being known even if the encryption method is known.
In addition to or instead of the encryption by means of an Exclusive-Or operation an asymmetrical encryption process can be used for encrypting the object information prior to transmission from the remote station to the central station, the open key being used for the encryption of the object information or the encrypted object information, decryption at the central station being effected by means of the secret key of the asymmetrical encryption process.
The invention further relates to a system for writing key information transmitted securely from a central station to a remote station into a data carrier available at said remote station, and to a data carrier and a terminal for use in such a system.